This invention relates to the technical field of an image processing method and apparatus that are suitable for use with digital photoprinters and so forth that obtain image data from pictures taken with cameras, that perform specified processing schemes on the obtained image data and that produce prints (photographs) as output image. The image processing method and apparatus are capable of correcting the distortion, chromatic aberration of magnification and deterioration of marginal lumination that occur in the pictures taken with inexpensive and low-performance cameras such as films with lens and compact cameras.
Heretofore, the images recorded on photographic films such as negatives and reversals (which are hereunder referred to simply as xe2x80x9cfilmsxe2x80x9d) have been commonly printed on light-sensitive materials (photographic paper) by means of direct (analog) exposure in which the film image is projected onto the light-sensitive material to achieve its areal exposure.
A new technology has recently been introduced and this is a printer that relies upon digital exposure. Briefly, the image recorded on a film is read photoelectrically, converted to digital signals and subjected to various image processing schemes to produce output image data for recording purposes; recording light modulated in accordance with the output image data is used to scan and expose a light-sensitive material to record a latent image, which is subsequently developed to produce a (finished) print. The printer operating on this principle has been commercialized as a digital photoprinter.
In the digital photoprinter, images can be processed as digital image data to determine the exposure conditions for printing, so various operations including the correction of washed-out highlights or flat (dull) shadows due to the taking of pictures with backlight or an electronic flash, sharpening and the correction of deteriorated marginal lumination can be effectively performed to produce prints of the high quality that has not been attainable by the conventional direct exposure technique.
If the pictures taken and recorded on the films are distorted, the quality of the output image on the prints cannot always be improved by the aforementioned corrective measures. There are three causes of the distorted pictures and they are chromatic aberration of magnification, distortion and deterioration of marginal lumination , i.e. reduction in brightness at the edge of image field, which are all due to the low performance of the lenses mounted on the cameras used to take the pictures.
Color images are typically formed of three primary colors, red (R), green (G) and blue (B). The refractive index (imaging magnification) of a lens varies subtly with the wavelength of light and R, G and B lights are imaged at different magnifications to cause xe2x80x9cchromatic aberration of magnificationxe2x80x9d. As a result, the image reproduced from the film has a definite color mismatch.
In order to obtain a satisfactory and appropriately recorded image, a plane of a scene of interest that is perpendicular to the optical axis must have an exact correspondence to the imaging plane, i.e., it must be imaged on the same plane perpendicular to the optical axis. In fact however, a single lens element has the imaging plane displaced along the optical axis and the resulting displacement of the imaging position in the axial direction causes a distortion of the imaged object. As a natural consequence, the reproduction of the image on the film is distorted.
Another problem with the pictures focused through the taking lens is that since the lens has such characteristics that the quantity of light decreases from the center of the image outward according to the so-called cosine4 law, the quantity of light at the edge of the image becomes insufficient to assure the desired brightness. This phenomenon is generally called xe2x80x9cdeteriorated marginal luminationxe2x80x9d.
Thus, due to the aberration characteristics of each taking lens, the output image becomes distorted and suffers from the problems of color mismatch, distortion and deteriorated marginal lumination.
In cameras such as a single-lens reflex camera that can compete at fairly high price, a plurality of high-precision lens elements are combined to ensure that various aberrations including chromatic aberration of magnification, distortion and deteriorated marginal lumination are effectively corrected to record appropriate images on the film. In contrast, low-performance and inexpensive cameras such as films with lens and compact cameras cannot afford the use of costly lenses and the images recorded on the film suffer from chromatic aberration of magnification, distortion and deteriorated marginal lumination. As a result, the images reproduced on prints become distorted.
To deal with this problem of image deterioration involving the difficulty in improving the quality of output images on prints, techniques have been proposed in connection with an image processing method and apparatus that correct image aberrations in accordance with the characteristics of lens aberrations that are obtained by a lens information acquisition device and a typical example of such technology is disclosed in Unexamined Published Japanese Patent Application (kokai) No. 281613/1997. According to this patent, the proposed technology can correct aberrations due to lenses and prevent the deterioration of image quality in the marginal area, thereby ensuring the production of high-quality images at all times.
However, if the information about the taking lens cannot be acquired preliminarily or if the information about the taking lens can be obtained but the aberration characteristics of the lens cannot, the aberrations due to the low performance of the taking lens, namely, the distortion, chromatic aberration of magnification and deteriorated marginal lumination, cannot be dealt with by the aforementioned technology and the deterioration of the output image cannot be prevented. Even if the lens-related information is obtained and corrective values for performing aberration corrections are selected automatically on the basis of this information, the intended aberration corrections cannot be fully performed and it sometimes occurs that the aberrational distortion remains in the corrected image, making it impossible to prevent image deterioration. In this case, the operator who intends to remove the aberrational distortion in the appropriate manner can rely upon his experience to determine the appropriate corrective values manually and perform the appropriate corrections.
In fact, however, the same operator does not always perform manual corrections and the corrective values that are used in manual corrections vary with the operator""s experience. This causes the problem that even if the same negative film is asked to be processed at one or more print output service shops, the desired prints cannot necessarily be obtained that have been given uniform and appropriate aberration corrections.
Conventionally, it is impossible for the operator to verify the image on the monitor after it has been corrected for aberrations and satisfactory prints cannot always be obtained unless a print is output from each of the corrected images to determine whether the correction is appropriate or not. However, this is not an efficient practice since it involves a waste of time and print outputs.
A further problem occurs if the information about the taking lens cannot be acquired preliminarily. Since corrective values cannot be obtained on the basis of the aberration characteristics of the lens, it becomes necessary to perform manual correction of the images in all frames of a roll of film. Although the same lens was used in taking the pictures and, hence, the aberration characteristics of the lens are fixed, the corrective values have to be set manually for each frame and the distorted image resulting from aberrations cannot appropriately be corrected in a rapid and efficient manner while assuring uniformity irrespective of which frames are processed.
The present invention has been accomplished under these circumstances and has as an object providing an image processing method which, even in the case where the correction of aberrations that was performed automatically on the basis of the information about the taking lens is inappropriate and must be enhanced by manual correction or in the case where corrective values cannot automatically be obtained on the basis of the aberration characteristics of the taking lens and must be replaced by manual correction, is capable of manual correction of distortion, chromatic aberration of magnification and deteriorated marginal lumination in a uniform and appropriate manner independently of the operator""s experience and other factors, and which guarantees an efficient and satisfactory finish without causing a waste of print outputs, and which, even in the case of performing manual operation on the images in all frames of a film that were taken with the same lens, employs the same corrective values to perform the same aberration correction, thereby ensuring that the images in all frames are output as prints after they have been corrected for the aberrations in an efficient, uniform and appropriate manner.
Another object of the invention is to provide an image processing apparatus that is suitable for implementing the above-described image processing method.
The first object of the invention can be attained by an image processing method according to its first aspect that obtains input image data from a picture optically taken with a taking lens and that performs specified processing schemes on the obtained input image data to obtain output image data suitable for producing an output image, which comprises the steps of: displaying a processed image on a monitor as it is reproduced from processed image data obtained by performing specified processing schemes on the input image data obtained from the picture; designating a portion of the processed image on the monitor to create a designated area in accordance with a state of an aberration in the processed image due to the taking lens; determining a corrective value for correcting the aberration based on an information in the input image data for the designated area; and correcting, based on the corrective value, the aberration on the input image data obtained from the picture and outputting the corrected image data.
The processed image is preferably one that is reproduced from the processed image data obtained by processing the input image data obtained from the picture such that initial correction of the aberration due to the taking lens is subjected based on an initial correcting value as determined by an information about the taking lens or a predetermined initial correcting value.
In another preferred embodiment, when the corrective value is determined based on the information in the input image data for the designated area, a provisional corrective value is determined for the input image data obtained from the picture and provisional correction is performed based on the provisional correction value to obtain provisionally corrected image data and, depending upon the state of the aberration in a provisionally corrected image, the provisional correcting value is cancelled and the provisionally corrected image data is reverted to the processed image data for the processed image.
In yet another preferred embodiment, the aberration is distortion based on the aberrations of the taking lens, the designated area is defined by a reference line which is either a horizontal line or a vertical line or both that are obtained by designating two points on the processed image and a designated point not lying on the reference line, and the step of determining the corrective value based on the information in the input image data for the designated area is for determining the corrective value for correcting the distortion by determining the correcting value based on the position information about the recorded subject such that the designated point comes to lie on the reference line as a result of correction.
In a further preferred embodiment, the aberration is chromatic aberration of magnification based on the aberrations of the taking lens, the designated area is created by designating the portion which involves a color mismatch caused by the chromatic aberration of magnification in the processed image, and the step of determining the corrective value based on the information in the input image data for the designated area is for determining the corrective value for correcting the chromatic aberration of magnification by first performing provisional correction on the input image data for the designated area, with the corrective value for use in correcting the chromatic aberration of magnification being varied, and then determining the corrective value based on the chromatic aberration of magnification of the processed image in the designated area after it has been corrected provisionally.
In another preferred embodiment, the aberration is deterioration of marginal lumination based on the aberrations of the taking lens, the designated area is a rectangular area within the processed image, that has at a center a single reference point designated from among four reference points that lie on two diagonals across the processed image and which are spaced from an intersection of the two diagonals by a specified distance toward corners of the processed image, and the step of determining the corrective value based on the information in the input image data for the designated area is for determining the corrective value for correcting the deterioration of the marginal lumination by first performing provisional correction on the input image data for the designated area, with the corrective value for use in correcting the deterioration of the marginal lumination being varied, and then determining the corrective value based on the deterioration of the marginal lumination of the processed image in the designated area after it has been corrected provisionally.
Preferably, the single reference point designated from among the four reference points is closest to a position on the processed image, that is designated for correcting the deterioration of the marginal lumination. The specified distance preferably ranges from 0.2 to 0.5 times length of the diagonals. More preferably, the specified distance is 0.35 times the length of the rectangles.
In yet another preferred embodiment, the picture is one that is subjected to image processing after another picture that was taken with the taking lens as same as what was used to take the picture and the predetermined initial corrective value was determined when correcting the aberrations due to the taking lens in the another image.
The second object of the invention can be attained by an image processing apparatus according to its second aspect that obtains input image data from an image optically taken with a taking lens and that performs specified processing schemes on the obtained input image data to obtain output image data suitable for producing an output image, comprising: information acquisition means for acquiring an information about the taking lens used to take the image; initial correcting means for performing on the input image data initial correction of an aberration due to the taking lens based on either an initial corrective value that is determined by the information about the taking lens that was obtained by the information acquisition means or a predetermined initial corrective value; a monitor for displaying an image that has been subjected to the initial correction; designating means by which a portion of the image that has been subjected to the initial correction is designated as a designated area on the monitor; and correcting means which, based on an image information about the designated area created by designation by the designating means, determines a corrective value for correcting the aberration and corrects the aberration in the taken image based on the corrective value.